Four Decades Old Retired NASA Satellite to Re-enter Atmosphere

New Delhi: In yet another example of the reentry of objects launched to space, a National Aeronautics and Space Administration (NASA) satellite was expected to reenter Earth’s atmosphere on January 8. According to a NASA release, the satellite was expected to reenter the atmosphere at around 6.40 PM Eastern Standard Time (EST) on January 8 with an uncertainty of 17 hours plus or minus. The satellite to reenter is the Earth Radiation Budget Satellite (ERBS) which was launched by NASA, USA, over four decades ago. For around 21 years out of the total time spent in space, ERBS investigated the absorption and radiation of energy from the Sun. However, NASA told that the risk of causing injuries to anyone by the vent is very low.

The satellite, weighing around 2,450 kilograms will burn most of its parts as it reenters the atmosphere, but some pieces will survive and hit the ground. ERBS was launched back in 1984 in the space shuttle Challenger aiming to study how much energy the Sun radiated and how much the Earth absorbed, along with it the satellite was purposed to study the ozone in the stratosphere. Although the reentry is expected in 2023, the ERBS retired in 2005. According to the orbital debris mitigation guidelines of NASA, with the latest update in 2019, the risk of casualties from the falling debris of any space object should not be greater than one in 10,000, which the ERBS is not going to meet. The NASA release says that the risk of casualties of the ERBS reentry is one in 9,400. However, it will meet the other criteria of the orbital debris mitigation guidelines, which say that any low Earth orbit satellite should not be deorbited more than 25 years after completing its mission. 

In a study published in September 2022, it was estimated that over the period 2010-2020, more than 600 objects larger than one-metre square reentered the Earth’s atmosphere without any control. The study also estimated that objects with a mass greater than 500 kg re-entered about every eight days during that period and those with weights greater than 2,000 kg re-entered every two weeks and those heavier than 5,000 kg re-entered once or twice a year.  The study warned that increasing space activities increases the risk of injuries. With the launch of satellites increasing, the study said that the risk associated with will be around 80% probability of having at least one victim per year.

Rockets, on the other hand, are bulkier than satellites and thus have a higher chance of surviving burns during reentry into the atmosphere. Hence, uncontrolled rocket re-entry also gets attention. Rockets are extensively used in space explorations to launch various objects like satellites into space. Parts of the rockets are often left in orbit, which can be a potential problem in the future. This is because the leftovers of the rockets, especially when in low enough orbit, can re-enter Earth’s atmosphere in an uncontrolled manner. Low Earth orbit is considered an Earth-centred orbit with an altitude of 2,000 km or less.

The uncontrolled re-entry of rockets holds the possibility of colliding with objects on Earth, including humans, aeroplanes or buildings. In fact, there have been past instances of leftover parts of rockets hitting objects on Earth and, in some cases, causing damage. Even though there have been no substantial casualties caused by such collisions, such events can potentially happen in the future.

A study published in Nature Astronomy a few months back assessed the likelihood of casualties posing a risk to human lives by such uncontrolled reentry of rockets. In their research, the team from the University of British Columbia, Canada, predicted that there is a chance of 6 to 10% that such events would cause casualties in the coming decade.

The research also highlighted that the major brunt of such events is expected to be disproportionately borne by the Global South, which indicates that prominent launching states bring risk to the rest of the world. Essentially, the people at greater risk of being affected by rocket debris belong to the countries that are not so active in space exploration.